1. Field of the Invention
The present invention relates to throttle valve assemblies of an automotive internal combustion engine. More specifically, the present invention relates to throttle valve assemblies of a type which has a traction control device for preventing skidding of driving wheels of the vehicle.
2. Description of the Prior Art
In general, a throttle valve assembly comprises a body forming an air intake passage led to the engine, a valve proper pivotally installed in a throttle chamber defined in the air intake passage and a valve actuating mechanism for actuating the valve proper in response to movement of an accelerator pedal. That is, in accordance with the movement of the accelerator pedal, the throttle valve is pivoted to control or adjust the air flow area of the throttle chamber thereby to control the output of the engine.
Nowadays, some of the throttle valve assemblies are of a type having a traction control device (or valve opening restricting device) which prevents skidding of driving wheels of the vehicle. Usually, the traction control device has a drive lever interposed between the valve actuating mechanism and the valve proper. The drive lever is driven by an electric motor. Upon receiving a control signal representing a certain running condition of the vehicle, the motor turns the drive lever in such a manner as to reduce the open degree of the valve proper more than that intended by the valve actuating mechanism. With this, the output of the engine is lowered and thus the driving torque applied to the driving wheels is temporarily reduced, resulting in prevention of the undesired skidding of the wheels.
However, due to its inherent construction, such throttle valve assembly tends to have the following drawback.
That is, in the traction control device as mentioned hereinabove, in order to restrict the open degree of the valve proper, the drive lever is turned by energizing the motor. Thus, if, with the open degree of the valve proper being restricted by a certain percent (for example, 50%) by the traction control device, the drive lever fails to operate due to damage of the motor or the like, the restriction of the open degree becomes fixed at such certain percent (50%) and thus thereafter the output of the engine is remarkably lowered. That is, the maximum output of the engine would be reduced to about 50% of the normal maximum power.